Background and purpose: Obstructive sleep apnea (OSA) is the most common type of sleep disorder which increases the risk of cardiovascular disease (CVD) and death. Despite the importance of OSA and its cardiovascular complications, most of the people with this disorder remain undiagnosed and untreated. The aim of this study was to evaluate the prevalence of at risk groups for OSA in cardiovascular patients.Materials and methods: This cross sectional study was performed in 400 patients with CVD (hypertension, heart failure, coronary arteries, valvular disease) admitted in critical care unit (CCU) in Sari Fatemeh Zahra Hospital, Iran 2016-2017. Data were collected by validated STOP-BANG, Epworth Sleepiness Scale (ESS), and the patients’ medical profiles. SPSS V20 was applied for data analysis.Results: The patients included 54% males (n=216). The mean age of patients was 62.99 ±11.53 years old. Among the patients 62.5% had high STOP-BANG scores. Patients with coronary disease (67%) and heart failure (66%) were at higher risk for OSA. There were no significant differences between the four groups of diseases investigated in the risk of developing OSA (P= 0.65). Compared with women, the majority of male patients were at high risk for OSA (86.5% vs 34.23%). Individuals with high risk of obstructive sleep apnea had the highest level of daytime sleepiness (P= 0.002).Conclusion: The risk of obstructive sleep apnea is high in cardiovascular patients, so, they should be investigated to prevent further complications.